Hadron Emission and Stopping in Heavy-Ion Collisions: Baryon-Rich Matter to Meson-Dominated Matter

Abstract

Today's accelerator facilities used for studies of relativistic heavy-ion collisions cover an energy range spanning over three orders of magnitude, from a few GeV up to a few TeV in center-of-mass energy per nucleon pair ($\sqrt{s_{NN}}$). We present a systematic overview of hadron emission in heavy-ion collisions across this entire energy range. The presented energy excitation functions of the approximated baryon and meson yields at mid-rapidity reflect the interplay between baryon stopping and particle production, both of which evolve continuously with increasing energy. At low energies (e.g., SIS18, AGS), strong nuclear stopping leads to high net-baryon densities at mid-rapidity and to the abundant formation of nuclear clusters. With increasing $\sqrt{s_{NN}}$, the relative baryon stopping power $\langle δy \rangle / y_p$ decreases, and meson production becomes dominant. The inelasticity, i.e. the fraction of the initial kinetic energy available converted in inelastic reactions into particle production and dynamics, is found to rise rapidly at low energies and then levels off at values around $0.7 - 0.8$. While at low energies up to $\sim 10$~GeV this available energy seems to be shared by equal amount between the production of new particles and the dynamics of the system, as well as radiation, the latter part starts to dominates at higher energies.